Mine does not have issues!
The preamp tube sockets are not the best after around of tube auditions, so take extra care in that regard!
Pignose G40V Project
Moderators: pompeiisneaks, Colossal
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Stevem
- Posts: 4574
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
K
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
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Littlewyan
- Posts: 1915
- Joined: Thu Sep 12, 2013 6:50 pm
- Location: UK
Re: Pignose G40V Project
Are your heater wires twisted? As mine just go straight from socket to socket, in the air as well.
I think one of the things that may save these amps is the .001uF Cap that dumps a lot of high end to ground after the tonestack. That will probably stop a lot of oscillation.
I think one of the things that may save these amps is the .001uF Cap that dumps a lot of high end to ground after the tonestack. That will probably stop a lot of oscillation.
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Stevem
- Posts: 4574
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
N
Yes, that's one of the things I did also was replace all the heater wiring with solid core well twisted stuff.
I also put down a layer of solder on the high current power supply traces after I cleaned off the mask , as those traces are pretty thin.
I also put down a layer of solder on the high current power supply traces after I cleaned off the mask , as those traces are pretty thin.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
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Littlewyan
- Posts: 1915
- Joined: Thu Sep 12, 2013 6:50 pm
- Location: UK
Re: Pignose G40V Project
Well I've just started stripping this thing down. Decided that it was easier to strip it all to install the new transformers. I have however just noticed that the chassis is rusting and am wondering if its worth carrying on.......
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Littlewyan
- Posts: 1915
- Joined: Thu Sep 12, 2013 6:50 pm
- Location: UK
Re: Pignose G40V Project
Ok I'm carrying on 
. Ordering new octal valve sockets. The noval sockets seem ok at the moment, possibly because it looks like the original valves are still in them!
I've basically stripped the whole thing down and am rewiring from scratch.
I've done some calculations and this thing should push out roughly 15W when its done. Should be just right for band practice
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. Ordering new octal valve sockets. The noval sockets seem ok at the moment, possibly because it looks like the original valves are still in them! I've basically stripped the whole thing down and am rewiring from scratch.
I've done some calculations and this thing should push out roughly 15W when its done. Should be just right for band practice
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Littlewyan
- Posts: 1915
- Joined: Thu Sep 12, 2013 6:50 pm
- Location: UK
Re: Pignose G40V Project
Its done! And it sounds great. Its a JCM800 preamp with a 6V6 power section. The power section is basically stock Marshall except the Presence control is the older style used in the early super leads.
Only issues are:
1. Bias resistor needs changing to move the range. I can only just bias the 6V6s to 65% dissipation at the moment.
2. It has bad parasitic oscillation with volumes on 10 and the treble and presence both on 10. Not a huge issue as I doubt I'll normally play it like that but I would like a bit more stability. Still, it turned out quieter than I thought it would.
3. Internal speaker is junk. Extremely bright with no definition at all. May replace with a Greenback G10.
Ill upload photos later as I can't upload them using my iPhone.
Only issues are:
1. Bias resistor needs changing to move the range. I can only just bias the 6V6s to 65% dissipation at the moment.
2. It has bad parasitic oscillation with volumes on 10 and the treble and presence both on 10. Not a huge issue as I doubt I'll normally play it like that but I would like a bit more stability. Still, it turned out quieter than I thought it would.
3. Internal speaker is junk. Extremely bright with no definition at all. May replace with a Greenback G10.
Ill upload photos later as I can't upload them using my iPhone.
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Littlewyan
- Posts: 1915
- Joined: Thu Sep 12, 2013 6:50 pm
- Location: UK
Re: Pignose G40V Project
Oh and a quick summary of what I did.
I stipped it to a bare chassis.
Sanded all paint off of inside and top of outside.
Converted preamp to JCM800. Only difference being the bright cap over the mixer resistor actually goes to the gain pot wiper. So its a bright cap as well. NFB is 100K resistor on 8Ohm tap.
Installed adjustable bias.
Replaced all filter caps, made it 50uf across the board with a 1K resistor instead of a choke.
Tidied up wiring a LOT!
And finally I installed a new PT and OT. So it now has a HT of 340V with 8K primary OT. Haven't measured power output yet but it should be roughly 10-15W.
I stipped it to a bare chassis.
Sanded all paint off of inside and top of outside.
Converted preamp to JCM800. Only difference being the bright cap over the mixer resistor actually goes to the gain pot wiper. So its a bright cap as well. NFB is 100K resistor on 8Ohm tap.
Installed adjustable bias.
Replaced all filter caps, made it 50uf across the board with a 1K resistor instead of a choke.
Tidied up wiring a LOT!
And finally I installed a new PT and OT. So it now has a HT of 340V with 8K primary OT. Haven't measured power output yet but it should be roughly 10-15W.
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Stevem
- Posts: 4574
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
M
Yup! If your going for more gain than stock you will likely need to sheild the input Jack and or the output Jack( s) .
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
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Littlewyan
- Posts: 1915
- Joined: Thu Sep 12, 2013 6:50 pm
- Location: UK
Re: Pignose G40V Project
I wouldn't say it has more gain, i've just spread it out a bit more instead of having most of it in the preamp. It does however have much more high end and upper mids now.
I think the Presence Control is actually wired wrong at present. I think the 0.1uf cap is between ground and the bottom of the presence pot. The presence pot is then wired as a variable resistor. Ill double check later but the control at present doesn't control high end, it just varies the feedback a bit.
I think the Presence Control is actually wired wrong at present. I think the 0.1uf cap is between ground and the bottom of the presence pot. The presence pot is then wired as a variable resistor. Ill double check later but the control at present doesn't control high end, it just varies the feedback a bit.
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Littlewyan
- Posts: 1915
- Joined: Thu Sep 12, 2013 6:50 pm
- Location: UK
Re: Pignose G40V Project
Ok the presence control isn't wired up the same way as the schematic. Apparently they changed it late production. So I've put the 4.7K resistor back and I've ordered a 22k pot to put in place of the 5K pot. So it will end up with a standard JCM800 Presence control.
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Littlewyan
- Posts: 1915
- Joined: Thu Sep 12, 2013 6:50 pm
- Location: UK
Re: Pignose G40V Project
PHOTOS AT LAST
These are just photos of the amp after the modification. I have attached one photo of it before just to show how the leads were all in the air, including the heater wiring.
These are just photos of the amp after the modification. I have attached one photo of it before just to show how the leads were all in the air, including the heater wiring.
You do not have the required permissions to view the files attached to this post.
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Littlewyan
- Posts: 1915
- Joined: Thu Sep 12, 2013 6:50 pm
- Location: UK
Re: Pignose G40V Project
Ok 20K pot installed (ordered 22k but was sent a 20k) and feedback resistor changed to 56K so it now has roughly the same amount of NFB as a 50W JCM800. With a 56K resistor it actually has a tad more NFB but thats ok as I think 6V6s overdrive bit easier than EL34s anyway.
I measured the amp and it puts out 10W clean, roughly 16W flat out. Should be just right for band practice as I normally attenuate my 67 Marshall down to 3W clean.
Oscillation at high settings has been tamed a bit, possibly by the extra NFB. I still need to go through the circuit with a scope.
I'm also looking to replace the stock speaker with a Celestion G10 Vintage.
I measured the amp and it puts out 10W clean, roughly 16W flat out. Should be just right for band practice as I normally attenuate my 67 Marshall down to 3W clean.
Oscillation at high settings has been tamed a bit, possibly by the extra NFB. I still need to go through the circuit with a scope.
I'm also looking to replace the stock speaker with a Celestion G10 Vintage.
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Stevem
- Posts: 4574
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
M
In regards to the oscillation issue, those speaker jacks are in a deadly location!
They are just like in the Orange TT amp that whenever I mod them for more gain , or even stuff in really big Gm rated preamp tubes I need to make up sheilding covers for the input and the 3 speaker output jacks out of insulative paper covered in Aluminum foil that's gets grounded and then you can open everthing up full with no problems !
Since you have free'ed up some room with the new PT you might move them to the bottom of the amp to the right of the output tubes and move the fuse block!
It's great fun trying to slide that chassis in and out of the stock cabinet no?
Holly crap could they have spared 1/32" more wood to make the dam cabinet a tad bigger, what a full on pain in the Ass!
They are just like in the Orange TT amp that whenever I mod them for more gain , or even stuff in really big Gm rated preamp tubes I need to make up sheilding covers for the input and the 3 speaker output jacks out of insulative paper covered in Aluminum foil that's gets grounded and then you can open everthing up full with no problems !
Since you have free'ed up some room with the new PT you might move them to the bottom of the amp to the right of the output tubes and move the fuse block!
It's great fun trying to slide that chassis in and out of the stock cabinet no?
Holly crap could they have spared 1/32" more wood to make the dam cabinet a tad bigger, what a full on pain in the Ass!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
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Littlewyan
- Posts: 1915
- Joined: Thu Sep 12, 2013 6:50 pm
- Location: UK
Re: Pignose G40V Project
Ah I didn't think of that. It is an extremely cramped chassis! Ill see what the scope picks up first before making any major mods. And yes, I LOVE removing this amp from the cab. I'm actually worried the cab will collapse when I remove the chassis. Might look at reinforcing it as it is a bit flimsy.
How are you finding the internal speaker? I'm still not sure what to replace it with. Vintage G10 looks good but I've heard a clip of it sounding a bit tinny.
How are you finding the internal speaker? I'm still not sure what to replace it with. Vintage G10 looks good but I've heard a clip of it sounding a bit tinny.
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Stevem
- Posts: 4574
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
T
Yup, I applyed some wood glue down into each seam on the cabinet .
I found that once a broke in the stock speaker for 12 hours on 60 HZ it was much better and I lined the cab with sound absorption material also, and this comes from a guy who is mostly into broken in Alinco drivers!
Of course it helps to do better than the two screws that hold that Amps baffle in too!
I found that once a broke in the stock speaker for 12 hours on 60 HZ it was much better and I lined the cab with sound absorption material also, and this comes from a guy who is mostly into broken in Alinco drivers!
Of course it helps to do better than the two screws that hold that Amps baffle in too!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!